CRC Implementations

crc16.c

#include <stdint.h>
#include <stdbool.h>

uint16_t crc16_ccit_FFFF(uint32_t len, uint8_t* data) {
    uint16_t crc = 0xFFFF;

    for (uint32_t i=0; i<len; i++) {
        uint16_t d = data[i];

        d ^= crc >> 8;
        d ^= d >> 4;
        crc = (crc << 8) ^ (d << 12) ^ (d << 5) ^ (d << 0);
    }

    return crc & 0xFFFF;
}

uint16_t crc16_ccit_xmodem(uint32_t len, uint8_t* data) {
    uint16_t crc = 0x0000;
    
    for (uint32_t i=0; i<len; i++) {
        uint16_t d = data[i];

        d ^= crc >> 8;
        d ^= d >> 4;
        crc = (crc << 8) ^ (d << 12) ^ (d << 5) ^ (d << 0);
    }

    return crc & 0xFFFF;
}

uint16_t crc16_ccit_kermit(uint32_t len, uint8_t* data) {
    uint16_t crc = 0x0000;

    for (uint32_t i=0; i<len; i++) {
        uint8_t d = data[i];
        uint16_t q;

        q = (crc ^ d) & 0x0f;
        crc = (crc >> 4) ^ (q * 0x1081);
        q = (crc ^ (d >> 4)) & 0xf;
        crc = (crc >> 4) ^ (q * 0x1081);
    }

    return (crc << 8) | (crc >> 8);
}